1. Field of the Invention
The present invention relates to an aqueous pigment dispersion containing a pigment as a coloring material, and an ink composition and an image forming method using the same.
2. Description of the Related Art
In recent years, water dispersions in which water-insoluble solids, such as pigments, are dispersed are frequently utilized for an inkjet recording ink and the like.
Water-based inks for inkjet recording has been required to have, as the quality, long-term stability in water resistance, lightfastness, stability over time of the dispersed particle diameter or precipitation stability during storage of dispersed particles, such as pigments dispersed and contained, or the like. In large-sized recording devices, such as an inkjet system for industrial application, an ink tank to be placed in the system is also large. Thus, after charging an ink, it is practically difficult to use the ink while shaking and mixing the ink according to the use timing. In such a system, long-term stability is particularly required, and it is essential for the ink stored in the tank to have stability for preventing precipitation. However, in the actual circumstances, most water-based inks are remarkably inferior to oil-based inks in terms of suitability with regard to pigment dispersibility and the like, and satisfactory quality is not obtained in respect of long-term storage stability or the like.
In order to solve such a problem, a water dispersion in which a pigment is coated with a resin having a polyether structure and having an acid value of 5 to 70 mgKOH/g has been proposed, for example (e.g., Japanese Patent No. 4109713). Moreover, an ink utilizing a pigment dispersion containing a water-insoluble vinyl polymer having an arylalkyl group or an aryl group and a pigment having a quinacridone skeleton has been proposed (e.g., Japanese Patent Application Laid-Open (JP-A) No. 2006-176623). Furthermore, recently, a water-based colored dispersion containing a polymer having a benzene ring indirectly linked to the main chain and having an acid value of from 10 mgKOH/g to less than 85 mgKOH/g has been proposed (e.g., JP-A No. 2009-84494).
However, also in any of the above techniques, long-term stability of the pigment dispersion or the inkjet recording ink is still insufficient, and when images are formed using the inks, there is a problem that a white deletion defect arises in the images.